In the present case, a lens should be understood to be a glass or plastic body having two optically effective, that is, light-refracting, surfaces situated opposite one another. A lens within the meaning of the invention is, in particular, a spectacle lens configured for insertion into a spectacle frame. In the present case, the term lens also encompasses so-called spectacle lens blanks, that is, a usually preformed material piece for producing a lens in a state before the end of surface processing, and also so-called semifinished products in the form of a lens blank having only one surface processed optically to completion. Such semifinished products are also designated as spectacle lens semifinished products.
In order to determine the spatial structure of objects, it is known, for example, to scan the objects in a coordinate measuring machine with a measuring sensor. In order that the spatial structure of an object can be ascertained in a pinpoint manner and with high accuracy in this way, it is necessary to capture a largest feasible number of measurement points by means of the measuring sensor at the surface of the object.
For the quality control of spectacle lenses in a spectacle lens manufacturing device, therefore, widespread use is made of measuring methods that measure a spectacle lens only at a few places. In order to ascertain the spatial structure and the optical properties of spectacle lenses, the latter are often examined by means of so-called vertex refractometers that measure the optical effect of the spectacle lenses in an arrangement in which light is passed through the spectacle lens (transmission measurement).